As the GM, do I need to read the Player's Guide or will I find every rule I need in the GM's book.
The books are pretty much self-contained, although the Player's Guide doesn't really have the detail on much of the rules that the GM's Guide has. If you have the time to read only one of the books, I would suggest the GM Guide for you, since you're the GM, but personally, I would read both books, as from the GM pov it's important enough to know what material the players have access to when they read the Player's Guide.
Hope that helps.
----- "You know, I am so constantly outwitting the opposition, I tend to forget the delight and satisfaction of the arts... the gentle art of fisticuffs." - The Doctor (The Romans)